JP4629178B2 - Nitride semiconductor device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a light emitting diode (LED), a laser diode (LD), a solar cell, a light emitting element such as an optical sensor, a light receiving element, or a nitride semiconductor (for example, In) used in an electronic device such as a transistor or a power device._XAl_YGa_1-XYN, 0 ≦ X, 0 ≦ Y, X + Y ≦ 1).
[0002]
[Prior art]
Nitride semiconductors have been put to practical use in various light sources such as full-color LED displays, traffic signal lights, and image scanner light sources as materials for high-intensity blue LEDs and pure green LEDs. These LED elements basically have a buffer layer made of GaN on a sapphire substrate, an n-side contact layer made of Si-doped GaN, and a single quantum well structure (SQW: Single-Quantum-Well) InGaN or InGaN. A multi-quantum well (MQW) active layer, a p-side cladding layer made of Mg-doped AlGaN, and a p-side contact layer made of Mg-doped GaN are sequentially stacked. At 20 mA, the blue LED with an emission wavelength of 450 nm shows 5 mW, the external quantum efficiency is 9.1%, the green LED with 520 nm has 3 mW, and the external quantum efficiency is 6.3%.
The multi-quantum well structure has a structure consisting of multiple minibands, and can efficiently emit light even with a small current. Therefore, improvement in device characteristics such as higher light output than a single quantum well structure is expected. The
For example, as an LED element using an active layer having a multiple quantum well structure, Japanese Patent Laid-Open No. 10-135514 discloses at least a barrier layer made of undoped GaN and an undoped InGaN in order to improve luminous efficiency and luminous intensity. There is disclosed a nitride semiconductor device having a light emitting layer having a multiple quantum well structure composed of a well layer and a cladding layer having a wider band gap than the barrier layer of the light emitting layer.
[0003]
[Problems to be solved by the invention]
However, the light emitting output is not sufficiently satisfactory in order to use the conventional element as an LED element for an illumination light source, an outdoor display exposed to direct sunlight, or the like. In this way, the active layer having a multiple quantum well structure can be considered to dramatically improve the light emission output, but it is difficult to fully exhibit its expected possibility.
Furthermore, a device made of a nitride semiconductor may deteriorate even at a voltage of 100 V, which is far weaker than static electricity generated in the human body due to its structure. For example, there is a risk of deterioration when taking out an antistatic bag or the like, or when applying it to a product. In order to further improve the reliability of the nitride semiconductor device, it is desired to eliminate the risk of such deterioration.
Therefore, an object of the present invention is to provide a nitride semiconductor light-emitting device that further improves the light emission output and enables the electrostatic withstand voltage to be increased by using an active layer having a multi-quantum well structure and extending the application range to various application products. Is to provide.
[0004]
[Means for Solving the Problems]
  That is, the present invention achieves the object of the present invention by the following configurations (1) to (6).
  (1) In a nitride semiconductor device having an n-side nitride semiconductor layer, an active layer, and a p-side nitride semiconductor layer on a substrate,
  The active layer is In_aGa_1-aA multiple quantum well structure including N (0 ≦ a <1) layers;
  The n-side nitride semiconductor layer is
  an n-side contact layer containing an n-type impurity;
  an n-side first multilayer film formed by laminating at least two types of nitride semiconductor layers having the same composition doped with n-type impurities at different concentrations;
  A first nitride semiconductor layer containing In, and an n-side second multilayer film layer in which a second nitride semiconductor layer having a composition different from that of the first nitride semiconductor layer is stacked,
Through the buffer layer on the substrateThe n-side contact layer;A nitride semiconductor device comprising the n-side first multilayer film layer, the n-side second multilayer film layer, and the active layer in this order.
  (2) A p-side multilayer clad layer in which the p-side nitride semiconductor layer is formed by stacking third and fourth nitride semiconductor layers having different band gap energies and different p-type impurity concentrations or the same. The nitride semiconductor device according to (1), comprising:
  (3) The p-side nitride semiconductor layer contains p-type impurities and Al_bGa_1-bThe nitride semiconductor device according to (1), further comprising a p-side single film clad layer made of N (0 ≦ b ≦ 1).
  (4) A first nitride semiconductor layer containing In between the n-side first multilayer film layer and the active layer, and a second nitride semiconductor having a composition different from that of the first nitride semiconductor layer The nitride semiconductor device according to any one of (1) to (3), which includes an n-side second multilayer film layer laminated with a layer..
  (5The nitride semiconductor device according to (1), wherein the n-side contact layer is formed on an undoped GaN layer.
  (6) In the nitride semiconductor device, the undoped GaN layer is grown at a low temperature._dAl_1-dA p-side GaN contact layer containing Mg as a p-type impurity is formed on the buffer layer made of N (0 <d ≦ 1) and further on the p-side multilayer clad layer or the p-side single layer clad layer. The nitride semiconductor device according to (5).
[0005]
That is, according to the present invention, the n-side first multilayer film composed of two or more types of nitride semiconductor layers having different n-type impurity concentrations on the n-side and the p-side the first multilayer film so as to sandwich the light emitting layer having the multiple quantum well structure. A p-side multilayer clad layer made of 3 and 4 nitride semiconductor layers or Al containing p-type impurities_bGa_1-bBy forming a p-side single film clad layer made of N (0 ≦ b ≦ 1) in combination, a nitride semiconductor device with improved luminous efficiency, improved luminous output, and further improved electrostatic withstand voltage is obtained. be able to.
Thus, by combining a plurality of nitride semiconductor layers having a specific composition or structure, the performance of the active layer having a multiple quantum well structure can be efficiently exhibited. Further, other nitride semiconductor layers preferable in combination with an active layer having a multiple quantum well structure are described below.
[0006]
In the present invention, a first nitride semiconductor layer containing In between the n-side first multilayer film layer and the active layer, and a second nitride having a composition different from that of the first nitride semiconductor layer It is preferable to have an n-side second multilayer film layered with a semiconductor layer because the luminous efficiency can be further improved and the luminous efficiency can be improved by lowering Vf.
Furthermore, in the present invention, it is preferable to have an n-side contact layer containing an n-type impurity on the substrate side from the n-side first multilayer film layer in order to improve the light emission output and lower Vf.
Furthermore, in the present invention, when the n-side contact layer is formed on the undoped GaN layer, the undoped GaN layer can be obtained as a layer having good crystallinity, so that the n-side serving as a layer for forming the n-electrode is formed. The crystallinity of the contact layer is improved, and the crystallinity of other nitride semiconductor layers such as an active layer formed on the n-side contact layer is improved, which is preferable for improving the light emission output.
Still further, in the present invention, the undoped GaN layer is grown at a low temperature._dAl_1-dWhen formed on a buffer layer composed of N (0 <d ≦ 1), the crystallinity of the undoped GaN layer is further improved, and the crystallinity of the n-side contact layer and the like is also improved, which is preferable in improving the light emission output. Furthermore, when an Mg-doped p-side GaN contact layer is formed on the p-side multilayer clad layer or the p-side single film clad layer, it becomes easier to obtain p-type characteristics and the p-side GaN contact layer It has good ohmic contact with the p-electrode formed thereon, and is preferable for improving the light emission output.
In the present invention, the total thickness of the undoped GaN layer, the n-side contact layer, and the n-side first multilayer film layer is 2 to 20 μm, preferably 3 to 10 μm, more preferably 4 to 9 μm. And it is preferable in terms of improvement in electrostatic withstand voltage. In addition, when the film thickness is in the above range, the element characteristics other than the electrostatic withstand voltage are good. The total film thickness of the three layers is appropriately adjusted so that the total film thickness of the three layers is within the above range within the preferable film thickness range of each layer.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail with reference to FIG. 1 which is a schematic cross-sectional view of a nitride semiconductor device showing the structure of a nitride semiconductor device according to an embodiment of the present invention.
FIG. 1 shows a substrate 1, a buffer layer 2, an undoped GaN layer 3, an n-side contact layer 4 containing n-type impurities, an n-side first multilayer film 5 containing n-type impurities, and first and second nitrides. An n-side second multilayer film layer 6 made of a semiconductor layer, an active layer 7 having a multiple quantum well structure, a p-side multilayer film clad layer 8 made of third and fourth nitride semiconductor layers, or a p-side single film clad layer 8 Mg doped p-side GaN contact layers 9 are sequentially stacked. Further, an n-electrode 11 is formed on the n-side contact layer 4, and a p-electrode 10 is formed on the p-side GaN contact layer 9.
[0008]
In the present invention, the substrate 1 includes SiC (6H, 4H, 3C) in addition to sapphire whose main surface is a sapphire C-plane, R-plane or A-plane, and other insulating substrates such as spinel (MgA12O4). ), A semiconductor substrate such as Si, ZnO, GaAs, or GaN can be used.
[0009]
In the present invention, the buffer layer 2 includes Ga_dAl_1-dA nitride semiconductor composed of N (where d is in the range of 0 <d ≦ 1). Preferably, the composition with a smaller proportion of Al exhibits a marked improvement in crystallinity, and more preferably a buffer layer composed of GaN. 2 is mentioned.
The film thickness of the buffer layer 2 is adjusted to a range of 0.002 to 0.5 μm, preferably 0.005 to 0.2 μm, and more preferably 0.01 to 0.02 μm. When the thickness of the buffer layer 2 is in the above range, the crystal morphology of the nitride semiconductor becomes good, and the crystallinity of the nitride semiconductor grown on the buffer layer 2 is improved.
The growth temperature of the buffer layer 2 is 200-900 degreeC, Preferably it adjusts in the range of 400-800 degreeC. When the growth temperature is in the above range, favorable polycrystals are obtained, and the crystallinity of the nitride semiconductor that grows on the buffer layer 2 as seed crystals is preferable.
The buffer layer 2 grown at such a low temperature may be omitted depending on the type of substrate, the growth method, and the like.
[0010]
Next, in the present invention, the undoped GaN layer 3 is a layer formed without adding an n-type impurity during growth. When the undoped GaN layer 3 is grown on the buffer layer 2, the crystallinity of the undoped GaN layer 3 is improved, and the crystallinity of the n-side contact layer 4 grown on the undoped GaN layer 3 is also improved. The film thickness of the undoped GaN layer 3 is 0.01 μm or more, preferably 0.5 μm or more, and more preferably 1 μm or more. The upper limit of the film thickness of the undoped GaN layer 3 is not particularly limited, but is appropriately adjusted in consideration of manufacturing efficiency and the like. When the film thickness is in the above range, the layers after the n-side contact layer 4 are preferably grown with good crystallinity. Furthermore, when the film thickness of the undoped GaN layer 3 is in the above range, the total film thickness of the n-side contact layer 4 and the n-side first multilayer film layer 5 is adjusted to the above range to improve the electrostatic withstand voltage. Is preferable.
[0011]
Next, in the present invention, the n-side contact layer 4 containing an n-type impurity contains 3 × 10 n-type impurities.¹⁸/ Cm^ThreeOr more, preferably 5 × 10¹⁸/ Cm^ThreeContains at the above concentration. Thus, if a large amount of n-type impurity is doped and this layer is used as an n-side contact layer, Vf and the threshold value can be lowered. When the impurity concentration deviates from the above range, Vf tends not to decrease. Further, when the n-side contact layer 4 is formed on the undoped GaN layer 3 having a low n-type impurity concentration and good crystallinity, the crystallinity is good despite having a high concentration of n-type impurities. Can be formed. The upper limit of the n-type impurity concentration of the n-side contact layer 4 is not particularly limited, but the limit of crystallinity that is too bad for the contact layer is 5 × 10.^{twenty one}/ Cm^ThreeThe following is desirable.
[0012]
The composition of the n-side contact layer 4 is In_eAl_fGa_1-efN (0 ≦ e, 0 ≦ f, e + f ≦ 1), the composition of which is not particularly limited, but preferably GaN, Al having an f value of 0.2 or less_fGa_1-fWhen N, a nitride semiconductor layer with few crystal defects is easily obtained. The thickness of the n-side contact layer 4 is not particularly limited, but is 0.1 to 20 μm, preferably 0.5 to 10 μm, more preferably 1 to 5 μm because it is a layer forming an n-electrode. When the film thickness is in the above range, the resistance value can be lowered, and the forward voltage of the light emitting element can be lowered, which is preferable. Furthermore, it is preferable that the film thickness of the n-side contact layer 4 is in the above range in terms of improving the electrostatic withstand voltage by the combination of the undoped GaN layer 3 and the n-side first multilayer film layer 5.
Further, the n-side contact layer 4 can be omitted when an n-side first multilayer film layer 5 described later is formed in a thick film.
[0013]
Next, in the present invention, the n-side first multilayer film layer 5 has the same composition in which n-type impurities are doped at different concentrations or different band gap energy or n-type impurities are doped at different concentrations. The multilayer film is formed by laminating at least two types of nitride semiconductor layers. The film thickness of the n-side first multilayer film 5 is 2 μm or less, preferably 1.5 μm or less, and more preferably 0.9 μm or less. Moreover, although a minimum is not specifically limited, For example, it is 0.05 micrometer or more. When the film thickness is within this range, it is preferable for improving the light emission output. Furthermore, it is preferable that the film thickness of the n-side first multilayer film layer 5 is in the above range in terms of improving electrostatic withstand voltage by a combination of the undoped GaN layer 3 and the n-side contact layer 4.
The fact that the nitride semiconductor layers constituting the multilayer film have different impurity concentrations is referred to as modulation doping. In this case, one of the layers is preferably not doped with impurities, that is, undoped.
[0014]
First, the case where the n-side first multilayer film layer 5 is a multilayer film formed by stacking at least two types of nitride semiconductor layers having different band gap energies will be described below.
The film thicknesses of the nitride semiconductor layer having a large band gap energy and the nitride semiconductor layer having a small band gap energy constituting the multilayer film layer of the n-side first multilayer film layer 5 are 100 angstroms or less, more preferably 70 angstroms or less, Most preferably, the film thickness is adjusted to 10 to 40 Å. When it is thicker than 100 angstroms, the nitride semiconductor layer having a large band gap energy and the nitride semiconductor layer having a small band gap energy have a film thickness exceeding the elastic strain limit, and tend to have minute cracks or crystal defects in the film. It is in. The lower limit of the thickness of the nitride semiconductor layer having a large band gap energy and the nitride semiconductor layer having a small band gap energy is not particularly limited, and may be one atomic layer or more, but is most preferably 10 angstroms or more as described above. .
[0015]
As described above, when the n-side first multilayer film 5 has a thin film structure, each film thickness of the nitride semiconductor layer constituting the multilayer film layer can be made not more than the elastic critical film thickness. A nitride semiconductor with very few crystal defects can be grown. Further, this multilayer film layer can stop crystal defects generated from the substrate through the undoped GaN layer 3 and the n-side contact layer 4 to some extent, and the n-side second multilayer film layer grown on the multilayer film layer. The crystallinity of 6 can be improved. Furthermore, there is an effect similar to HEMT.
[0016]
The nitride semiconductor layer having a large band gap energy is a nitride semiconductor containing at least Al, preferably Al._gGa_1-gIt is desirable to grow N (0 <g ≦ 1). On the other hand, the nitride semiconductor having a small band gap energy may be any nitride semiconductor having a lower band gap energy than a nitride semiconductor having a large band gap energy, but preferably Al._hGa_1-hN (0 ≦ h <1, g> h), In_jGa_1-jA binary mixed crystal or ternary mixed crystal nitride semiconductor such as N (0 ≦ j <1) is easy to grow, and a crystal with good crystallinity is easily obtained. Among them, a nitride semiconductor having a large band gap energy is particularly preferably an Al containing substantially no In._gGa_1-gN (0 <g <1), and a nitride semiconductor having a small band gap energy is substantially free of Al._jGa_1-jN (0 ≦ j <1), and for the purpose of obtaining a multilayer film excellent in crystallinity, Al having an Al mixed crystal ratio (g value) of 0.3 or less_gGa_1-gThe combination of N (0 <g ≦ 0.3) and GaN is most preferable.
[0017]
Further, when the n-side first multilayer film layer 5 forms a clad layer as an optical confinement layer and a carrier confinement layer, it is necessary to grow a nitride semiconductor having a larger band gap energy than the well layer of the active layer. The nitride semiconductor layer having a large band gap energy is a nitride semiconductor having a high Al mixed crystal ratio. Conventionally, when a nitride semiconductor having a high Al mixed crystal ratio is grown as a thick film, cracks are easily generated, and thus crystal growth is very difficult. However, when the n-side first multilayer film layer 5 is a multilayer film layer as in the present invention, even if the single layer constituting the multilayer film layer is a layer having a slightly higher Al mixed crystal ratio, the film thickness is less than the critical elastic film thickness. Since it is grown, it is hard to crack. Therefore, since a layer having a high Al mixed crystal ratio can be grown with good crystallinity, the optical confinement effect and the carrier confinement effect are enhanced, and the threshold voltage in the laser element and Vf (forward voltage) in the LED element can be lowered.
[0018]
Furthermore, it is preferable that the n-type impurity concentration of the nitride semiconductor layer having a large band gap energy and the nitride semiconductor layer having a small band gap energy of the n-side first multilayer film layer 5 are different. This is called so-called modulation doping. When the n-type impurity concentration of one layer is low, preferably when the impurity is not doped (undoped) and the other is highly doped, the threshold voltage, Vf, etc. are lowered. be able to. This is because when a layer having a low impurity concentration is present in the multilayer film layer, the mobility of the layer is increased, and a layer having a high impurity concentration is also present at the same time. By being able to form a layer. In other words, a layer having a high impurity concentration and a high mobility and a layer having a high impurity concentration and a high carrier concentration are present at the same time. It is assumed that Vf decreases.
[0019]
When doping a nitride semiconductor layer having a large band gap energy with a large amount of n-type impurities, a preferable doping amount to the nitride semiconductor layer having a large band gap energy is 1 × 10¹⁷/cm^Three~ 1x10²⁰/cm^ThreeMore preferably 1 × 10¹⁸/cm^Three~ 5x10¹⁹/cm^ThreeAdjust to the range. 1 × 10¹⁷/cm^ThreeIs less than the nitride semiconductor layer having a small band gap energy, it tends to be difficult to obtain a layer having a high carrier concentration.²⁰/cm^ThreeIf it is more, the leakage current of the element itself tends to increase. On the other hand, the n-type impurity concentration of the nitride semiconductor layer having a small band gap energy should be less than that of the nitride semiconductor layer having a large band gap energy, and preferably 1/10 or less. Most preferably, when undoped, a layer with the highest mobility is obtained, but since the film thickness is thin, there is an n-type impurity diffused from the side of the nitride semiconductor having a large band gap energy, and the amount is 1 × 10¹⁹/cm^ThreeThe following is desirable. As the n-type impurity, elements of Group IVB and VIB of the periodic table such as Si, Ge, Se, S, and O are selected. Preferably, Si, Ge, and S are n-type impurities. This effect is the same when the nitride semiconductor layer having a large band gap energy is doped with a small amount of n-type impurities and the nitride semiconductor layer having a small band gap energy is doped with a large amount of n-type impurities.
As described above, the case where the multilayer film layer is preferably modulation-doped with impurities has been described. However, the impurity concentrations of the nitride semiconductor layer having a large band gap energy and the nitride semiconductor layer having a small band gap energy can be made equal.
[0020]
Furthermore, in the nitride semiconductor layer constituting the multilayer film of the n-side first multilayer film layer, the impurity-doped layer has a high impurity concentration near the center of the semiconductor layer with respect to the thickness direction. It is desirable that the impurity concentration in the vicinity of the portion be small (preferably undoped). More specifically, for example, when a multilayer film is formed of AlGaN doped with Si as an n-type impurity and an undoped GaN layer, AlGaN is doped with Si, so that electrons are emitted as a donor to the conduction band. Electrons fall into the low-potential GaN conduction band. Since the GaN crystal is not doped with a donor impurity, it is not subject to carrier scattering by the impurity. Therefore, the electrons can easily move in the GaN crystal, and the substantial mobility of electrons increases. This is similar to the effect of the two-dimensional electron gas, in which the substantial mobility in the electron lateral direction is increased and the resistivity is decreased. Further, the effect is further enhanced when the n-type impurity is doped at a high concentration in the central region of AlGaN having a large band gap energy. That is, depending on the electrons moving in GaN, the n-type impurity ions (Si in this case) contained in AlGaN are somewhat scattered. However, if both ends are undoped with respect to the thickness direction of the AlGaN layer, it is difficult to receive Si scattering, and the mobility of the undoped GaN layer is further improved.
[0021]
Next, the case where the n-side first multilayer film layer 5 is formed by stacking nitride semiconductor layers having the same composition, and n-type impurities are doped at different concentrations between the nitride semiconductor layers will be described.
First, the nitride semiconductor constituting the n-side first multilayer film layer 5 is not particularly limited and may have the same composition, but preferably includes GaN. When the n-side first multilayer film layer 5 is made of GaN, it can grow with good crystallinity when it is made of ternary mixed crystal rather than ternary mixed crystal, and the crystallinity of the nitride semiconductor that is grown thereafter also becomes good. preferable.
The n-side first multilayer film layer 5 having the same composition, for example, GaN includes a first GaN layer containing n-type impurities and a second GaN layer having a concentration different from the n-type impurity concentration of the first GaN layer, Preferably, it has a multilayer film structure composed of at least two types of nitride semiconductors, one of which is an undoped GaN layer. When the modulation-doped multi-layer structure is formed as described above, the n-side first multi-layer film layer 5 has the same effect as that of the case where the n-side first multi-layer film 5 is composed of at least two kinds of layers which are different in the band gap energy and are modulation-doped. can get.
The concentration of the n-side impurity is 1 × 10¹⁷~ 1x10^{twenty one}/ Cm^Three, Preferably 1 × 10¹⁸~ 1x10¹⁹/ Cm^Three, More preferably 3 × 10¹⁸~ 7 × 10¹⁸/ Cm^ThreeIt is. In this case, the total thickness of the n-side first multilayer film layer 5 is not particularly limited, but is 1000 to 4000 angstroms, preferably 2000 to 3000 angstroms. Each thickness of the multilayer film is 500 angstroms or less, preferably 200 angstroms or less, more preferably 100 angstroms or less, and the lower limit of the film thickness is not particularly limited, but may be one atomic layer or more, but 10 angstroms or more. Is preferred. When the film thickness is as described above, it is possible to grow with good crystallinity, which is preferable for improving the light emission output.
[0022]
Further, the n-side first multilayer film layer 5 composed of two or more layers having different bandgap energy or the same composition and different impurity concentration as described above can also serve as the n-side contact layer. In this case, the film thickness of the n-side first multilayer film layer 5 is 0.5 to 4 μm, preferably 1 to 3 μm, more preferably 2 to 2.8 μm. In this case, the thickness of the n-side first multilayer film layer 5 is adjusted by the above-described at least two types of nitride semiconductor layers. In this case, each film thickness constituting the n-side first multilayer film layer 5 may be a multilayer film layer within the above-mentioned range, and the entire film thickness may be the n-side first film thickness when serving as the n-side contact layer. If it is the range of the said film thickness of 1 multilayer film layer 5, you may adjust with two or more types of nitride semiconductors in which each film thickness exceeds the said range.
[0023]
Next, in the present invention, the n-side second multilayer film layer 6 includes a first nitride semiconductor layer containing In, a second nitride semiconductor layer having a composition different from that of the first nitride semiconductor layer, Are stacked, and the film thickness of at least one of the first nitride semiconductor layer and the second nitride semiconductor layer is 100 angstroms or less. Preferably, both the first nitride semiconductor layer and the second nitride semiconductor layer are 100 angstroms or less, more preferably 70 angstroms or less, and most preferably 50 angstroms or less. By reducing the film thickness in this way, the multilayer film layer has a superlattice structure, and the crystallinity of the multilayer film layer is improved, so that the output tends to be improved.
Here, it is preferable to combine the n-side first multilayer film layer and the n-side second multilayer film layer to improve light emission output and lower forward voltage (Vf). The reason for this is not clear, but it is considered that the crystallinity of the active layer grown on the n-side second multilayer layer is improved.
[0024]
The first nitride semiconductor layer is In_kGa_1-kN (0 <k <1), and the second nitride semiconductor layer is In_mGa_1-mMost preferred is N (0 ≦ m <1, m <k), preferably GaN.
[0025]
Furthermore, the film thickness of at least one of the first nitride semiconductor layer or the second nitride semiconductor layer is different between adjacent first nitride semiconductor layers or second nitride semiconductor layers. Or the same. Also. The layers having different thicknesses are different from each other when the first nitride semiconductor layer or the multilayer film layer in which a plurality of second nitride semiconductor layers are stacked is formed. It means that the film thicknesses of the first nitride semiconductor layer (second nitride semiconductor layer) sandwiching the first nitride semiconductor layer are different from each other.
[0026]
Furthermore, the first nitride semiconductor layer or the second nitride semiconductor in which the composition of at least one group III element in the first nitride semiconductor layer or the second nitride semiconductor layer is close to each other. The compositions of the same group III element in the layer are preferably different from each other. This is because the second nitride semiconductor layer (first nitride semiconductor layer) is formed when a multilayer film layer in which a plurality of first nitride semiconductor layers or second nitride semiconductor layers are stacked is formed. It means that the composition ratios of Group III elements of the sandwiched first nitride semiconductor layer (second nitride semiconductor layer) are different from each other.
[0027]
The n-side second multilayer film layer 6 may be formed apart from the active layer, but is most preferably formed in contact with the active layer. The output tends to be improved more easily when it is formed in contact with the active layer.
[0028]
The first nitride semiconductor layer and the second nitride semiconductor layer of the n-side second multilayer film layer 6 are preferably undoped. Undoped refers to a state where impurities are not intentionally doped. For example, impurities mixed by diffusion from adjacent nitride semiconductor layers are also referred to as undoped in the present invention. Note that impurities mixed by diffusion often have a gradient in impurity concentration in the layer.
[0029]
Either the first nitride semiconductor layer or the second nitride semiconductor layer may be doped with an n-type impurity. This is called modulation doping, and the output tends to be improved by modulation doping. As n-type impurities, group IV and group VI elements such as Si, Ge, Sn, and S are preferably selected, and Si and Sn are more preferably used.
[0030]
In addition, both the first nitride semiconductor layer and the second nitride semiconductor layer may be doped with n-type impurities. When doping an n-type impurity, the impurity concentration is 5 × 10^{twenty one}/cm^ThreeOr less, preferably 1 × 10²⁰/cm^ThreeAdjust to: 5 × 10^{twenty one}/cm^ThreeIf it exceeds the upper limit, the crystallinity of the nitride semiconductor layer deteriorates, and the output tends to decrease. The same applies to modulation doping.
[0031]
As shown in FIG. 1, the n-side nitride semiconductor layer below the active layer 7 includes a first nitride semiconductor layer containing In, and a first nitride semiconductor layer having a composition different from that of the first nitride semiconductor layer. It has the n side 2nd multilayer film layer 6 by which two nitride semiconductor layers were laminated. In the n-side second multilayer film layer 6, at least one first nitride semiconductor layer and at least one second nitride semiconductor layer are formed, for a total of two or more layers, preferably three or more layers, more preferably at least one each. It is desirable to laminate two or more layers and laminate four or more layers in total.
When the n-side second multilayer film layer 6 is formed in contact with the active layer, the multilayer film layer in contact with the first layer (well layer or barrier layer) of the active layer may be the first nitride semiconductor layer, Any of the two nitride semiconductor layers may be used, and the stacking order of the n-side second multilayer film layer 6 is not particularly limited. In FIG. 1, the n-side second multilayer film layer 6 is formed in contact with the active layer 7, but another n-type nitride is interposed between the n-side second multilayer film layer 6 and the active layer. You may have the layer which consists of semiconductors.
The film thickness of at least one of the first nitride semiconductor layer or the second nitride semiconductor layer constituting the n-side second multilayer film layer is 100 angstroms or less, preferably 70 angstroms or less, more preferably 50 angstroms or less. By doing so, the thin film layer becomes less than the elastic critical film thickness, the crystal is improved, the crystallinity of the first or second nitride semiconductor layer stacked thereon is improved, and the crystallinity of the entire multilayer film layer is improved. Therefore, the output of the element is improved.
[0032]
The first nitride semiconductor layer is a nitride semiconductor containing In, preferably ternary mixed crystal In_kGa_1-kN (0 <k <1), more preferably an In value with a k value of 0.5 or less_kGa_1-kN, most preferably an In value of 0.2 or less_kGa_1-kN. On the other hand, the second nitride semiconductor layer may be a nitride semiconductor having a composition different from that of the first nitride semiconductor layer, and is not particularly limited. In order to grow the second nitride semiconductor having good crystallinity, When a binary mixed crystal or a ternary mixed crystal nitride semiconductor having a band gap energy larger than that of the first nitride semiconductor is grown, and GaN among them is grown, a multilayer film layer having good crystallinity can be grown as a whole. Therefore, the most preferable combination is that the first nitride semiconductor layer has an In value with a k value of 0.5 or less._kGa_1-kN, and the second nitride semiconductor layer is a combination with GaN.
[0033]
The film thicknesses of the first and second nitride semiconductor layers are set to 100 angstroms or less, preferably 70 angstroms or less, more preferably 50 angstroms or less. By setting the film thickness of the single nitride semiconductor layer to 100 angstroms or less, the nitride semiconductor single layer has an elastic critical film thickness or less, and a nitride semiconductor with better crystallinity is grown as compared with the case of growing with a thick film. it can. Further, by setting both to 70 angstroms or less, the n-side second multilayer film layer 6 has a superlattice (multilayer film) structure, and when an active layer is grown on this highly crystalline multilayer film structure, The second multilayer layer 6 acts like a buffer layer, so that the active layer can grow with good crystallinity.
[0034]
Furthermore, it is also preferable that the film thickness of at least one of the first or second nitride semiconductor layers is different between adjacent first or second nitride semiconductor layers. For example, when the first nitride semiconductor layer is InGaN and the second nitride semiconductor layer is GaN, the thickness of the InGaN layer between the GaN layer and the GaN layer is gradually increased as it approaches the active layer. Since the refractive index changes inside the multilayer film layer by thinning or reducing the thickness, a layer in which the refractive index gradually changes can be formed. That is, the same effect as that of forming a nitride semiconductor layer having a substantially composition gradient can be obtained. For this reason, in an element that requires an optical waveguide, such as a laser element, the mode of the laser beam can be adjusted by forming a waveguide with this multilayer film layer.
[0035]
Further, the composition of at least one group III element in the first or second nitride semiconductor layer is different from each other in the composition of the same group III element in the adjacent first or second nitride semiconductor layer. Or the same. For example, when the composition of the same group III element is different from each other, when the first nitride semiconductor layer is InGaN and the second nitride semiconductor layer is GaN, the InGaN layer between the GaN layer and the GaN layer By gradually increasing or decreasing the In composition of the layer as it approaches the active layer, the refractive index is changed inside the multilayer film layer, and the nitride semiconductor is substantially compositionally graded, as in the previous embodiment. A layer can be formed. The refractive index tends to decrease as the In composition decreases.
[0036]
Both the first and second nitride semiconductor layers may be undoped, both may be doped with n-type impurities, or one of them may be doped with impurities. In order to improve crystallinity, undoped is most preferable, followed by modulation doping and then both doping. When both are doped with n-type impurities, the n-type impurity concentration of the first nitride semiconductor layer and the n-type impurity concentration of the second nitride semiconductor layer may be different.
[0037]
In the present invention, the active layer 7 having a multiple quantum well structure is a nitride semiconductor containing In and Ga, preferably In._aGa_1-aIt is formed of N (0 ≦ a <1), and may be either n-type or p-type. However, undoped (no impurity added) is preferable because strong inter-band light emission is obtained and the half-value width of the emission wavelength is narrowed. The active layer 7 may be doped with n-type impurities and / or p-type impurities. When the active layer 7 is doped with an n-type impurity, the interband emission intensity can be further increased as compared with the undoped layer. When the active layer 7 is doped with a p-type impurity, the peak wavelength can be shifted to the energy side lower by about 0.5 eV than the peak wavelength of interband light emission, but the half width becomes wider. When both the p-type impurity and the n-type impurity are doped in the active layer, the emission intensity of the active layer doped only with the p-type impurity can be further increased. In particular, when an active layer doped with a p-type dopant is formed, it is preferable that the conductivity type of the active layer is doped with an n-type dopant such as Si to make the whole n-type. Non-doping is most preferred for growing an active layer with good crystallinity.
[0038]
The order of stacking of the barrier layer and the well layer of the active layer 7 is not particularly limited, and is stacked from the well layer and ends with the well layer, stacked from the well layer and ends with the barrier layer, stacked from the barrier layer and ended with the barrier layer. It may end, or may be stacked from the barrier layer and end with the well layer. The thickness of the well layer is adjusted to 100 angstroms or less, preferably 70 angstroms or less, more preferably 50 angstroms or less. The upper limit of the thickness of the well layer is not particularly limited, but is 1 atomic layer or more, preferably 10 angstroms or more. If the well layer is thicker than 100 angstroms, the output tends to be difficult to improve.
On the other hand, the thickness of the barrier layer is adjusted to 2000 angstroms or less, preferably 500 angstroms or less, more preferably 300 angstroms or less. The upper limit of the thickness of the barrier layer is not particularly limited, but is 1 atomic layer or more, preferably 10 angstroms or more. It is preferable that the barrier layer is in the above range because the output is easily improved. Further, the film thickness of the entire active layer 7 is not particularly limited, and the total film thickness of the active layer 7 is adjusted by adjusting the number of layers and the stacking order of the barrier layers and well layers in consideration of a desired wavelength of the LED element and the like. Adjust.
[0039]
In the present invention, the p-side cladding layer 8 is formed by laminating a third nitride semiconductor layer having a large band gap energy and a fourth nitride semiconductor layer having a band gap energy smaller than that of the third nitride semiconductor layer. Alternating layers having different p-type impurity concentrations, or the same multilayer film layer, or Al containing p-type impurities_bGa_1-bIt is a single layer made of N (0 ≦ b ≦ 1).
First, the case where the p-side cladding layer 8 is a p-side multilayer cladding layer having a multilayer structure (superlattice structure) will be described below.
The film thickness of the third and fourth nitride semiconductor layers constituting the multilayer film layer of the p-side multilayer film cladding layer 17 is 100 angstroms or less, more preferably 70 angstroms or less, and most preferably 10 to 40 angstroms. The film thicknesses of the third nitride semiconductor layer and the fourth nitride semiconductor layer may be the same or different. When each film thickness of the multilayer structure is within the above range, the nitride semiconductor becomes less than the critical critical film thickness of the nitride semiconductor, and a nitride semiconductor with better crystallinity can be grown compared to the case of growing with a thick film. Since the crystallinity of the layer is improved, when a p-type impurity is added, a p-layer having a large carrier concentration and a low resistivity is obtained, and the Vf and threshold value of the device tend to be lowered. A multilayer film layer is formed by laminating two kinds of layers having such a thickness as a pair a plurality of times. The total film thickness of the p-side multilayer clad layer 8 is adjusted by adjusting the film thicknesses of the third and fourth nitride semiconductor layers and adjusting the number of laminations. The total film thickness of the p-side multilayer clad layer 8 is not particularly limited, but is 2000 angstroms or less, preferably 1000 angstroms or less, more preferably 500 angstroms or less. If the total film thickness is within this range, the light emission output is high. The forward voltage (Vf) is preferably reduced.
The third nitride semiconductor layer is a nitride semiconductor containing at least Al, preferably Al_nGa_1-nIt is desirable to grow N (0 <n ≦ 1), and the fourth nitride semiconductor is preferably Al_pGa_1-pN (0 ≦ p <1, n> p), In_rGa_1-rIt is desirable to grow a binary mixed crystal or ternary mixed crystal nitride semiconductor such as N (0 ≦ r ≦ 1).
When the p-side cladding layer 8 has a superlattice structure, the crystallinity is improved, the resistivity tends to decrease, and Vf tends to decrease.
[0040]
A case where the third nitride semiconductor layer and the fourth nitride semiconductor layer have different p-type impurity concentrations in the p-type impurity concentration of the p-side multilayer clad layer 8 will be described below.
The third nitride semiconductor layer and the fourth nitride semiconductor layer of the p-side multilayer clad layer 8 have different p-type impurity concentrations, with one layer having a large impurity concentration and the other layer having a low impurity concentration. To do. Similar to the n-side cladding layer 12, the p-type impurity concentration of the fourth nitride semiconductor layer having a smaller band gap energy is increased by increasing the p-type impurity concentration of the third nitride semiconductor layer having the larger band gap energy. If the value is small, preferably undoped, the threshold voltage, Vf, etc. can be lowered. The reverse is also possible. That is, the p-type impurity concentration of the third nitride semiconductor layer having a large band gap energy may be decreased, and the p-type impurity concentration of the fourth nitride semiconductor layer having a small band gap energy may be increased.
[0041]
A preferred doping amount to the third nitride semiconductor layer is 1 × 10¹⁸/cm^Three~ 1x10^{twenty one}/cm^ThreeMore preferably 1 × 10¹⁹/cm^Three~ 5x10²⁰/cm^ThreeAdjust to the range. 1 × 10¹⁸/cm^ThreeLess than the fourth nitride semiconductor layer, the layer having a high carrier concentration tends to be difficult to obtain.^{twenty one}/cm^ThreeWhen the amount is more than 1, the crystallinity tends to deteriorate. On the other hand, the p-type impurity concentration of the fourth nitride semiconductor layer should be less than that of the third nitride semiconductor layer, and preferably 1/10 or less. Most preferably, when undoped, a layer with the highest mobility can be obtained, but since the film thickness is small, there is a p-type impurity diffused from the third nitride semiconductor side, and the amount thereof is 1 × 10²⁰/cm^ThreeThe following is desirable. The same applies to the case where the third nitride semiconductor layer having a large band gap energy is doped with a small amount of p-type impurities and the fourth nitride semiconductor layer having a small band gap energy is doped with a large amount of p-type impurities.
As the p-type impurities, Group IIA and IIB elements of the periodic table such as Mg, Zn, Ca and Be are selected, and preferably Mg, Ca and the like are used as p-type impurities.
[0042]
Furthermore, in the nitride semiconductor layer constituting the multilayer film, the layer doped with impurities at a high concentration has a large impurity concentration near the center of the semiconductor layer and a small impurity concentration near both ends in the thickness direction ( It is desirable to reduce the resistivity.
[0043]
When the p-type impurity concentrations of the third nitride semiconductor layer and the fourth nitride semiconductor layer of the p-side multilayer clad layer 8 are the same, the p-type impurities of the third and fourth nitride semiconductor layers are used. The impurity concentration is adjusted within the range of the p-type impurity concentration of the third nitride semiconductor layer when the concentrations are different. Thus, when the p-type impurity concentration is the same, the crystallinity tends to be slightly inferior to the case where the impurity concentration is different, but it becomes easier to form the p-type cladding layer 8 having a high carrier concentration and the output is improved. This is preferable.
[0044]
Next, the p-side cladding layer 8 contains p-type impurities and Al_bGa_1-bIn the case of a single layer composed of N (0 ≦ b ≦ 1), the thickness of the p-side single film cladding layer 8 is 2000 angstroms or less, preferably 1000 angstroms or less, more preferably 500-100 angstroms or less. is there. When the film thickness is within the above range, the light emission output is improved and Vf is preferably lowered. The composition of the p-side single film cladding layer 8 is Al_bGa_1-bN (0 ≦ b ≦ 1).
The single-layer clad layer can be grown with good crystallinity in combination with the first multilayer film layer 4 although the crystallinity is slightly inferior to the p-side clad layer having the multilayer structure. It is possible to reduce the threshold value and Vf. Furthermore, even when a single film is combined with other layer structures, the performance of the device is reduced, and since it is a single film, the manufacturing process can be simplified, which is preferable for mass production.
The p-type impurity concentration of the p-side single film cladding layer 8 is 1 × 10¹⁸~ 1x10^{twenty one}/cm^Three, Preferably 5 × 10¹⁸~ 5x10²⁰/cm^Three, More preferably 5 × 10¹⁹~ 1x10²⁰/cm^ThreeIt is. It is preferable that the impurity concentration is in the above range because a good p-type film can be obtained.
[0045]
Next, in the present invention, the Mg-doped p-side GaN contact layer 9 is composed of a binary mixed crystal nitride semiconductor containing no In or Al. If In and Al are contained, ohmic contact with the p electrode 10 cannot be obtained, and the light emission efficiency is lowered. The film thickness of the p-side contact layer 9 is 0.001 to 0.5 μm, preferably 0.01 to 0.3 μm, more preferably 0.05 to 0.2 μm. If the film thickness is less than 0.001 μm, it becomes easy to electrically short-circuit the p-type GaAlN cladding layer, and it is difficult to act as a contact layer. In addition, since a binary mixed crystal GaN contact layer having a different composition is laminated on a ternary mixed crystal GaAlN cladding layer, conversely, if the film thickness is made thicker than 0.5 μm, a misfit between the crystals may occur. Lattice defects are likely to occur in the p-side GaN contact layer 9 and the crystallinity tends to decrease. Note that the thinner the contact layer, the lower the Vf and the better the light emission efficiency. If the p-type impurity of the p-type GaN contact layer 9 is Mg, p-type characteristics are easily obtained, and ohmic contact is easily obtained. Mg concentration is 1 × 10¹⁸~ 1x10^{twenty one}/cm^Three, Preferably 5 × 10¹⁹~ 3x10²⁰/cm^Three, More preferably 1 × 10²⁰/cm^ThreeDegree. When the Mg concentration is within this range, a good p-type film can be easily obtained, and Vf is preferable.
[0046]
The n-electrode 11 is formed on the n-side contact layer 4, and the p-electrode is formed on the Mg-doped p-side GaN contact layer 9. The material for the n electrode and the p electrode is not particularly limited. For example, W / Al can be used as the n electrode, and Ni / Au can be used as the p electrode.
[0047]
【Example】
Examples which are one embodiment of the present invention are shown below, but the present invention is not limited thereto.
[Example 1]
A first embodiment will be described with reference to FIG.
The substrate 1 made of sapphire (C-plane) is set in a MOVPE reaction vessel, and the temperature of the substrate is raised to 1050 ° C. while flowing hydrogen to clean the substrate.
[0048]
(Buffer layer 2)
Subsequently, the temperature is lowered to 510 ° C., hydrogen is used as a carrier gas, ammonia and TMG (trimethyl gallium) are used as a source gas, and a buffer layer 2 made of GaN is grown on the substrate 1 to a thickness of about 150 Å.
[0049]
(Undoped GaN layer 3)
After the growth of the buffer layer 2, only TMG is stopped and the temperature is raised to 1050 ° C. When the temperature reaches 1050 ° C., TMG and ammonia gas are similarly used as the source gas, and the undoped GaN layer 3 is grown to a thickness of 1.5 μm.
[0050]
(N-side contact layer 4)
Subsequently, at 1050 ° C., similarly, TMG, ammonia gas, and silane gas are used as source gas and silane gas as impurity gas.¹⁸/cm^ThreeAn n-side contact layer 4 made of doped GaN is grown to a thickness of 2.25 μm.
[0051]
(N-side first multilayer film layer 5)
Next, the silane gas alone was stopped, and at 1050 ° C., TMG and ammonia gas were used to grow an undoped GaN layer with a film thickness of 75 Å, and then silane gas was added at the same temperature to add Si to 4.5 × 10 6.¹⁸/cm^ThreeA doped GaN layer is grown to a thickness of 25 Angstroms. In this manner, a pair consisting of an A layer composed of an undoped GaN layer of 75 angstroms and a 25 angstrom B layer having an Si doped GaN layer is grown. Then, 25 pairs are stacked so as to have a thickness of 2500 Å, and the n-side first multilayer film layer 5 made of a multilayer film having a superlattice structure is grown.
[0052]
(N-side second multilayer layer 6)
Next, at the same temperature, a second nitride semiconductor layer made of undoped GaN is grown to 40 Å, and then the temperature is set to 800 ° C., and TMG, TMI, and ammonia are used._0.13Ga_0.87A first nitride semiconductor layer made of N is grown by 20 Å. Then, these operations are repeated, and 10 layers are alternately stacked in the order of 2 + 1 and finally, the n-side formed of a multi-layer film having a superlattice structure in which a second nitride semiconductor layer made of GaN is grown by 40 angstroms. The second multilayer layer 6 is grown to a thickness of 640 angstrom.
[0053]
(Active layer 7)
Next, a barrier layer made of undoped GaN is grown to a thickness of 200 angstroms, and subsequently the temperature is set to 800 ° C., and TMG, TMI, and ammonia are used to undoped In._0.4Ga_0.6A well layer made of N is grown to a thickness of 30 Å. Then, an active layer 7 having a multi-quantum well structure having a total film thickness of 1120 angstroms is formed by alternately laminating five barrier layers and four well layers in the order of barrier + well + barrier + well. Grow.
[0054]
(P-side multilayer clad layer 8)
Next, TMG, TMA, ammonia, Cp2Mg (cyclopentadienylmagnesium) was used at a temperature of 1050 ° C., and Mg was 1 × 10²⁰/cm^ThreeDoped p-type Al_0.2Ga_0.8A third nitride semiconductor layer made of N is grown to a thickness of 40 angstroms, followed by a temperature of 800 ° C., and TMG, TMI, ammonia and Cp 2 Mg are used to make Mg 1 × 10²⁰/cm^ThreeDoped In_0.03Ga_0.97A fourth nitride semiconductor layer made of N is grown to a thickness of 25 Å. Then, these operations are repeated, and 5 layers are alternately stacked in the order of 3 + 4, and finally, the third nitride semiconductor layer is grown to a thickness of 40 angstroms and is formed of a superlattice multilayer film. The side multilayer clad layer 8 is grown to a film thickness of 365 angstroms.
[0055]
(P-side GaN contact layer 9)
Subsequently, at 1050 ° C., TMG, ammonia, and Cp 2 Mg were used, and Mg was 1 × 10²⁰/cm^ThreeA p-side contact layer 9 made of doped p-type GaN is grown to a thickness of 700 angstroms.
[0056]
After completion of the reaction, the temperature is lowered to room temperature, and the wafer is annealed in a reaction vessel at 700 ° C. in a nitrogen atmosphere to further reduce the resistance of the p-type layer.
[0057]
After annealing, the wafer is taken out from the reaction vessel, a mask having a predetermined shape is formed on the surface of the uppermost p-side contact layer 9, and etching is performed from the p-side contact layer side with an RIE (reactive ion etching) apparatus. As shown in FIG. 1, the surface of the n-side contact layer 4 is exposed.
[0058]
After etching, a translucent p-electrode 10 containing Ni and Au having a thickness of 200 angstroms is formed on almost the entire surface of the p-side contact layer as the uppermost layer, and a p-pad electrode made of Au for bonding on the p-electrode 10 11 is formed to a thickness of 0.5 μm. On the other hand, an n-electrode 12 containing W and Al was formed on the surface of the n-side contact layer 4 exposed by etching to obtain an LED element.
[0059]
This LED element emits pure green light of 520 nm at a forward current of 20 mA, Vf is 3.5 V, which is nearly 1.0 V lower than the conventional multi-quantum well structure LED element, and the output is It improved to 2.0 times or more. For this reason, an LED having substantially the same characteristics as a conventional LED element at 10 mA was obtained. Furthermore, the electrostatic withstand voltage is 1.3 times or more than the conventional one, which is favorable.
[0060]
The configuration of the conventional LED element is the same as in Example 1, except that the second buffer layer made of undoped GaN, the n-side contact layer made of Si-doped GaN, and the first quantum layer made of GaN. Active layer with well structure, single Mg-doped Al_0.1Ga_0.9An N layer and a p-side contact layer made of Mg-doped GaN are sequentially stacked.
[0061]
[Example 2]
An LED element was fabricated in the same manner as in Example 1 except that the active layer 7 was changed as follows.
(Active layer 7)
Next, a barrier layer made of undoped GaN is grown to a thickness of 250 angstrom, and subsequently the temperature is set to 800 ° C., and TMG, TMI, and ammonia are used to undoped In_0.3Ga_0.7A well layer made of N is grown to a thickness of 30 Å. Then, 7 barrier layers and 6 well layers are alternately stacked in the order of barrier + well + barrier + well... + Barrier, and an active layer 7 having a multiple quantum well structure having a total film thickness of 1930 angstroms. Grow.
The obtained LED element showed pure blue light emission of 470 nm at a forward current of 20 mA, and good results were obtained as in Example 1.
[0062]
[Example 3]
An LED element was fabricated in the same manner as in Example 1 except that the active layer 7 was changed as follows.
(Active layer 7)
Next, a barrier layer made of undoped GaN is grown to a thickness of 250 angstrom, and subsequently the temperature is set to 800 ° C., and TMG, TMI, and ammonia are used to undoped In_0.3Ga_0.7A well layer made of N is grown to a thickness of 30 Å. The active layer 7 having a multiple quantum well structure with a total thickness of 1650 angstroms is formed by alternately stacking 6 barrier layers and 5 well layers in the order of barrier + well + barrier + well. Grow.
The obtained LED element showed pure blue light emission of 470 nm at a forward current of 20 mA, and good results were obtained as in Example 1.
[0063]
[Example 4]
An LED element was fabricated in the same manner as in Example 1 except that the active layer 7 was changed as follows.
(Active layer 7)
Next, a barrier layer made of undoped GaN is grown to a thickness of 250 angstrom, and subsequently the temperature is set to 800 ° C., and TMG, TMI, and ammonia are used to undoped In_0.35Ga_0.65A well layer made of N is grown to a thickness of 30 Å. Then, 7 barrier layers and 6 well layers are alternately stacked in the order of barrier + well + barrier + well... + Barrier, and an active layer 7 having a multiple quantum well structure having a total film thickness of 1930 angstroms. Grow.
The obtained LED element emits 500 nm of blue-green light at a forward current of 20 mA, and good results are obtained as in Example 1.
[0064]
[Example 5]
An LED element was fabricated in the same manner as in Example 1 except that the active layer 7 was changed as follows.
(Active layer 7)
Next, a barrier layer made of undoped GaN is grown to a thickness of 250 angstrom, and subsequently the temperature is set to 800 ° C., and TMG, TMI, and ammonia are used to undoped In_0.35Ga_0.65A well layer made of N is grown to a thickness of 30 Å. Then, four barrier layers and three well layers are alternately stacked in the order of barrier + well + barrier + well... + Barrier, and an active layer 7 having a multiple quantum well structure with a total film thickness of 1090 angstroms. Grow.
The obtained LED element emits 500 nm of blue-green light at a forward current of 20 mA, and good results are obtained as in Example 1.
[0065]
[Example 6]
An LED device was manufactured in the same manner as in Example 1 except that the n-side second multilayer film layer 6 was not grown.
The obtained LED element has a good light output compared to the conventional LED element although the element characteristics and the light output are slightly lower than those of Example 1.
[0066]
[Example 7]
An LED device was fabricated in the same manner as in Example 1, except that the p-side multilayer clad layer 8 was changed as follows.
(P-side single film clad layer 8)
Using TMG, TMA, ammonia, Cp2Mg (cyclopentadienylmagnesium) at a temperature of 1050 ° C., Mg is 1 × 10²⁰/cm^ThreeDoped p-type Al_0.16Ga_0.84A p-side single film clad layer 8 made of N is grown to a thickness of 300 Å.
Although the obtained LED element is grown as a single layer without using the superlattice as a cladding layer, the combination with the other layer constitutions is slightly inferior to the performance of Example 1, but almost the same good results. can get. In addition, a single layer is preferable because the manufacturing process can be simplified as compared with the case of using a multilayer film layer.
[0067]
[Example 8]
An LED element was fabricated in the same manner as in Example 1 except that the n-side first multilayer film layer 5 was changed as follows.
(N-side first multilayer film layer 5)
An A layer made of an undoped GaN layer is grown to a thickness of 100 Å, and Si is 1 × 10¹⁸/ Cm^ThreeDoped Al_0.1Ga_0.9The n-side first multilayer film layer 5 is grown to a thickness of 2500 angstroms by stacking 20 pairs of the A layer and the B layer obtained by growing a B layer of N with a film thickness of 25 angstroms.
The obtained LED element has substantially the same characteristics as in Example 1, and good results are obtained.
[0068]
[Example 9]
An LED element was fabricated in the same manner as in Example 1 except that the n-side contact layer 4 was changed as follows.
(N-side contact layer 4)
At 1050 ° C., TMG, ammonia gas as source gas, silane gas as impurity gas, Si 4.5 × 10¹⁸/cm^ThreeAn n-side contact layer 4 made of doped GaN is grown to a thickness of 6 μm.
The obtained LED element has substantially the same characteristics as in Example 1, and good results are obtained.
[0069]
[Example 10]
In Example 1, three kinds of LED elements are manufactured in the same manner except that the film thickness of the n-side contact layer 4 is 4.25 μm, 5.25 μm, and 7.25 μm.
The obtained LED element has substantially the same characteristics as in Example 1, and good results are obtained. In addition, when the film thickness is 4.25 μm and 5.25 μm, the electrostatic withstand voltage and the like are slightly in the example. Better than 1.
[0070]
[Example 11]
In Example 1, the n-side second multilayer film layer 6 is a second nitride semiconductor layer made of undoped GaN, and Si is doped with 5 × 10 17 / cm 3._0.13Ga_0.87An LED element is fabricated in the same manner except that a multilayer film composed of a first nitride semiconductor layer made of N is used.
The obtained LED element exhibits substantially the same characteristics as in Example 1.
[0071]
[Example 12]
In Example 1, the p-side multilayer clad layer 8 is made of 5 × 10 5 Mg.¹⁹/ Cm^ThreeDoped Al_0.2Ga_0.8A third nitride semiconductor layer made of N, and undoped In_0.03Ga_0.97An LED element is fabricated in the same manner except that a multilayer film composed of a fourth nitride semiconductor layer made of N is used.
The obtained LED element exhibits substantially the same characteristics as in Example 1.
[0072]
[Example 13]
In Example 1, the p-side multilayer clad layer 8 is made of undoped Al._0.2Ga_0.8A third nitride semiconductor layer made of N; and 5 × 10 5 of Mg¹⁹/ Cm^ThreeDoped In_0.03Ga_0.97An LED element is fabricated in the same manner except that a multilayer film composed of a fourth nitride semiconductor layer made of N is used.
The obtained LED element exhibits substantially the same characteristics as in Example 1.
[0073]
【The invention's effect】
The nitride semiconductor device of the present invention can effectively exhibit the possibility of an active layer having a multiple quantum well structure by combining an active layer having a multiple quantum well structure with the specific layer configuration described above. It is possible to improve the light emission output and the electrostatic withstand voltage.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view showing the structure of an LED element according to an embodiment of the present invention.
[Explanation of symbols]
1 ... sapphire substrate,
2 ... buffer layer,
3 ... undoped GaN layer,
4 ... n-side contact layer,
5 ... n-side first multilayer film layer,
6 ... n-side second multilayer film layer,
7 ... active layer,
8 ... p-side cladding layer,
9: Mg-doped p-side GaN contact layer,
10 ... p electrode,
11: n electrode.

Claims (6)

In a nitride semiconductor device having an n-side nitride semiconductor layer, an active layer, and a p-side nitride semiconductor layer on a substrate,
The active layer has a multiple quantum well structure including an In _a Ga _1-a N (0 ≦ a <1) layer;
The n-side nitride semiconductor layer is
an n-side contact layer containing an n-type impurity;
an n-side first multilayer film formed by laminating at least two types of nitride semiconductor layers having the same composition doped with n-type impurities at different concentrations;
A first nitride semiconductor layer containing In, and an n-side second multilayer film layer in which a second nitride semiconductor layer having a composition different from that of the first nitride semiconductor layer is stacked,
The nitride semiconductor comprising the n-side contact layer, the n-side first multilayer film layer, the n-side second multilayer film layer, and the active layer in this order on the substrate via a buffer layer element.   The p-side nitride semiconductor layer includes a p-side multilayer clad layer in which third and fourth nitride semiconductor layers having different band gap energy and different p-type impurity concentrations or the same third and fourth nitride semiconductor layers are laminated. The nitride semiconductor device according to claim 1, wherein: 2. The nitridation according to claim 1, wherein the p-side nitride semiconductor layer includes a p-side single film clad layer containing p-type impurities and made of Al _b Ga _1-b N (0 ≦ b ≦ 1). Semiconductor device.   A first nitride semiconductor layer containing In and a second nitride semiconductor layer having a composition different from that of the first nitride semiconductor layer are provided between the n-side first multilayer film layer and the active layer. The nitride semiconductor device according to any one of claims 1 to 3, further comprising an n-side second multilayer film layer stacked. The nitride semiconductor device according to claim 1 , wherein the n-side contact layer is formed on an undoped GaN layer. In the nitride semiconductor device, the undoped GaN layer is formed on a buffer layer made of Ga _d Al _1-d N (0 <d ≦ 1) grown at a low temperature, and further the p-side multilayer clad layer or the p-side 6. The nitride semiconductor device according to claim 5 , wherein a p-side GaN contact layer containing Mg as a p-type impurity is formed on the single film clad layer.

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